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<title>Struct template matches</title>
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<a name="boost.proto.matches"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct template matches</span></h2>
<p>boost::proto::matches &#8212; A Boolean metafunction that evaluates whether a given expression type matches a grammar.</p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../proto/reference.html#header.boost.proto.matches_hpp" title="Header &lt;boost/proto/matches.hpp&gt;">boost/proto/matches.hpp</a>&gt;

</span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> Grammar<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="matches.html" title="Struct template matches">matches</a> <span class="special">:</span> <span class="keyword"></span> mpl::bool_&lt;<em class="replaceable"><code>true-or-false</code></em>&gt; <span class="special">{</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp136855696"></a><h2>Description</h2>
<p>
            <code class="computeroutput">proto::matches&lt;Expr, Grammar&gt;</code> inherits from
            <code class="computeroutput">mpl::true_</code> if
            <code class="computeroutput">Expr::proto_grammar</code> matches
            <code class="computeroutput">Grammar::proto_grammar</code>, and from
            <code class="computeroutput">mpl::false_</code> otherwise.
          </p>
<p>
            Non-terminal expressions are matched against a grammar according to the following rules:
            </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem"><p>
                  The wildcard pattern, <code class="computeroutput">
                    <a class="link" href="_.html" title="Struct _">proto::_</a>
                  </code>, matches any expression.
                </p></li>
<li class="listitem"><p>
                  An expression
                  <code class="computeroutput">
                    <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a>&lt;AT,
                    <a class="link" href="listN.html" title="Struct template listN">
                      proto::listN
                    </a>&lt;A<sub>0</sub>,...A<sub>n</sub>&gt;
                    &gt;
                  </code>
                  matches a grammar
                  <code class="computeroutput">
                    <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a>&lt;BT,
                    <a class="link" href="listN.html" title="Struct template listN">
                      proto::listN
                    </a>&lt;B<sub>0</sub>,...B<sub>n</sub>&gt;
                    &gt;
                  </code> if
                  <code class="computeroutput">BT</code> is <code class="computeroutput">
                    <a class="link" href="_.html" title="Struct _">proto::_</a>
                  </code> or
                  <code class="computeroutput">AT</code>, and if <code class="computeroutput">
                    A<sub>x</sub>
                  </code> matches
                  <code class="computeroutput">
                    B<sub>x</sub>
                  </code> for each <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>.
                </p></li>
<li class="listitem"><p>
                  An expression
                  <code class="computeroutput">
                    <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a>&lt;AT,
                    <a class="link" href="listN.html" title="Struct template listN">
                      proto::listN
                    </a>&lt;A<sub>0</sub>,...A<sub>n</sub>,U<sub>0</sub>,...U<sub>m</sub>&gt;
                    &gt;
                  </code> matches a grammar
                  <code class="computeroutput">
                    <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a>&lt;BT,
                    <a class="link" href="listN.html" title="Struct template listN">
                      proto::listM
                    </a>&lt;B<sub>0</sub>,...B<sub>n</sub>,<a class="link" href="vararg.html" title="Struct template vararg">proto::vararg</a>&lt;V&gt;
                    &gt; &gt;
                  </code> if
                  <code class="computeroutput">BT</code> is <code class="computeroutput">
                    <a class="link" href="_.html" title="Struct _">proto::_</a>
                  </code> or
                  <code class="computeroutput">AT</code>, and if
                  <code class="computeroutput">
                    A<sub>x</sub>
                  </code> matches
                  <code class="computeroutput">
                    B<sub>x</sub>
                  </code> for each
                  <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code> and if
                  <code class="computeroutput">
                    U<sub>x</sub>
                  </code> matches
                  <code class="computeroutput">V</code> for each <code class="computeroutput">x</code> in
                  <code class="computeroutput">[0,m]</code>.
                </p></li>
<li class="listitem"><p>
                  An expression <code class="computeroutput">E</code> matches
                  <code class="computeroutput">
                    <a class="link" href="or_.html" title="Struct template or_">proto::or_</a>&lt;B<sub>0</sub>,...B<sub>n</sub>&gt;
                  </code> if
                  <code class="computeroutput">E</code> matches some
                  <code class="computeroutput">
                    B<sub>x</sub>
                  </code> for
                  <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>.
                </p></li>
<li class="listitem"><p>
                  An expression <code class="computeroutput">E</code> matches
                  <code class="computeroutput">
                    <a class="link" href="and_.html" title="Struct template and_">proto::and_</a>&lt;B<sub>0</sub>,...B<sub>n</sub>&gt;
                  </code> if
                  <code class="computeroutput">E</code> matches all
                  <code class="computeroutput">
                    B<sub>x</sub>
                  </code> for
                  <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>.
                </p></li>
<li class="listitem">
<p>
                  An expression <code class="computeroutput">E</code> matches
                  <code class="computeroutput">
                    <a class="link" href="if_.html" title="Struct template if_">proto::if_</a>&lt;T,U,V&gt;
                  </code> if:
                  </p>
<div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
<code class="computeroutput">
                        boost::result_of&lt;<a class="link" href="when.html" title="Struct template when">proto::when</a>&lt;<a class="link" href="_.html" title="Struct _">proto::_</a>,T&gt;(E)&gt;::type::value
                      </code>
                      is <code class="computeroutput">true</code> and
                      <code class="computeroutput">E</code> matches
                      <code class="computeroutput">U</code>, <span class="emphasis"><em>or</em></span>
</li>
<li class="listitem">
<code class="computeroutput">
                        boost::result_of&lt;<a class="link" href="when.html" title="Struct template when">proto::when</a>&lt;<a class="link" href="_.html" title="Struct _">proto::_</a>,T&gt;(E)&gt;::type::value
                      </code>
                      is <code class="computeroutput">false</code> and <code class="computeroutput">E</code> matches
                      <code class="computeroutput">V</code>.
                    </li>
</ul></div>
<p>
                  Note: <code class="computeroutput">U</code> defaults to <code class="computeroutput">
                    <a class="link" href="_.html" title="Struct _">proto::_</a>
                  </code>
                  and <code class="computeroutput">V</code> defaults to
                  <code class="computeroutput">
                    <a class="link" href="not_.html" title="Struct template not_">proto::not_</a>&lt;<a class="link" href="_.html" title="Struct _">proto::_</a>&gt;
                  </code>.
                </p>
</li>
<li class="listitem"><p>
                  An expression <code class="computeroutput">E</code> matches
                  <code class="computeroutput">
                    <a class="link" href="not_.html" title="Struct template not_">proto::not_</a>&lt;T&gt;
                  </code> if
                  <code class="computeroutput">E</code> does <span class="emphasis"><em>not</em></span> match <code class="computeroutput">T</code>.
                </p></li>
<li class="listitem"><p>
                  An expression <code class="computeroutput">E</code> matches
                  <code class="computeroutput">
                    <a class="link" href="switch_.html" title="Struct template switch_">proto::switch_</a>&lt;C, T&gt;
                  </code> if
                  <code class="computeroutput">E</code> matches <code class="computeroutput">C::case_&lt;boost::result_of&lt;<a class="link" href="when.html" title="Struct template when">proto::when</a>&lt;<a class="link" href="_.html" title="Struct _">proto::_</a>,T&gt;(E)&gt;::type&gt;</code>.
                  Note: <code class="computeroutput">T</code> defaults to <code class="computeroutput"><a class="link" href="tag_of.html" title="Struct template tag_of">proto::tag_of</a>&lt;<a class="link" href="_.html" title="Struct _">proto::_</a>&gt;()</code>
                </p></li>
</ul></div>
<p>
          </p>
<p>
            A terminal expression can trivially match the grammar <a class="link" href="_.html" title="Struct _">proto::_</a>. In addition,
            a terminal expression
            <code class="computeroutput">
              <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a>&lt;AT,
              <a class="link" href="term.html" title="Struct template term">proto::term</a>&lt;A&gt; &gt;
            </code> matches a grammar
            <code class="computeroutput">
              <a class="link" href="basic_expr.html" title="Struct template basic_expr">proto::basic_expr</a>&lt;BT, <a class="link" href="term.html" title="Struct template term">proto::term</a>&lt;B&gt; &gt;
            </code>
            if <code class="computeroutput">BT</code> is <code class="computeroutput"><a class="link" href="_.html" title="Struct _">proto::_</a></code>
            or <code class="computeroutput">AT</code> and one of the following is true:
            </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem"><p>
                  <code class="computeroutput">B</code> is the wildcard pattern,
                  <code class="computeroutput">
                    <a class="link" href="_.html" title="Struct _">proto::_</a>
                  </code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">A</code> is <code class="computeroutput">B</code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">A</code> is <code class="computeroutput">B &amp;</code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">A</code> is <code class="computeroutput">B const &amp;</code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">B</code> is <code class="computeroutput">
                    <a class="link" href="exact.html" title="Struct template exact">proto::exact</a>&lt;A&gt;
                  </code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">B</code> is
                  <code class="computeroutput">
                    <a class="link" href="convertible_to.html" title="Struct template convertible_to">proto::convertible_to</a>&lt;X&gt;
                  </code>
                  and <code class="computeroutput">boost::is_convertible&lt;A,X&gt;::value</code> is
                  <code class="computeroutput">true</code>.
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">A</code> is <code class="computeroutput">X[M]</code> or
                  <code class="computeroutput">X(&amp;)[M]</code> and
                  <code class="computeroutput">B</code> is <code class="computeroutput">
                    X[<a class="link" href="N.html" title="Global N">proto::N</a>]
                  </code>.
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">A</code> is <code class="computeroutput">X(&amp;)[M]</code>
                  and <code class="computeroutput">B</code> is <code class="computeroutput">
                    X(&amp;)[<a class="link" href="N.html" title="Global N">proto::N</a>]
                  </code>.
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">A</code> is <code class="computeroutput">X[M]</code> or
                  <code class="computeroutput">X(&amp;)[M]</code> and <code class="computeroutput">B</code> is
                  <code class="computeroutput">X*</code>.
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">B</code> <em class="replaceable"><code>lambda-matches</code></em>
                  <code class="computeroutput">A</code> (see below).
                </p></li>
</ul></div>
<p>
          </p>
<p>
            A type <code class="computeroutput">B</code> <em class="replaceable"><code>lambda-matches</code></em>
            <code class="computeroutput">A</code> if one of the following is true:
            </p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem"><p>
                  <code class="computeroutput">B</code> is <code class="computeroutput">A</code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">B</code> is the wildcard pattern, <code class="computeroutput">
                    <a class="link" href="_.html" title="Struct _">proto::_</a>
                  </code>
                </p></li>
<li class="listitem"><p>
                  <code class="computeroutput">B</code> is <code class="computeroutput">
                    T&lt;B<sub>0</sub>,...B<sub>n</sub>&gt;
                  </code> and <code class="computeroutput">A</code> is <code class="computeroutput">
                    T&lt;A<sub>0</sub>,...A<sub>n</sub>&gt;
                  </code> and for each <code class="computeroutput">x</code> in <code class="computeroutput">[0,n]</code>,
                  <code class="computeroutput">A<sub>x</sub></code> and
                  <code class="computeroutput">B<sub>x</sub></code> are types such that
                  <code class="computeroutput">A<sub>x</sub></code> <em class="replaceable"><code>lambda-matches</code></em>
                  <code class="computeroutput">B<sub>x</sub></code>
                </p></li>
</ul></div>
<p>
          </p>
</div>
</div>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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